1. Field of the Invention
This invention relates to apparatus and a noninvasive method for determining the oxygen-saturation of hemoglobin in the blood vessels of the fundus of the eye (human or animal). Specifically, it relates to the determination of the degree of hemoglobin oxygenation in the vasculature of the retina while the eye is dark (scoptic vision) or light-adapted (photopic vision). This technique can reveal subtle alternations in visual function which are not discernible with method currently available.
2. Description of the Prior Art
Optical methods for determining the degree of hemoglobin oxygenation, or oxygen saturation, in the blood vessels in the human eye are know to the art. Such methods are employed to diagnose early pathogenic states in the eye.
U.S. Pat. No. 4,305,398 discloses an oximeter for measuring the oxygen saturation of the blood in the fundus of the human eye using four different wavelengths. The reflected light outputs are compared at these wavelengths and the degree of oxygen saturation is calculated by suitable arithmetic operations.
U.S. Pat. No. 4,253,744 relates to an optical system for the measurement of pulse waves in the artery of the eye fundus or oxygen saturation therein. Light for illuminating the eye fundus is converged on the cornea and enters through pupil. Light reflected at the surface of the cornea is converged and blocked at its converging position while the light reflected from the eye fundus is allowed to pass by the light blocking member to reach a photocell.
U.S. Pat. No. 4,848,897 discloses an ophthalmic diagnosis apparatus having an optical spatial frequency filter and a double diffraction optical system generating two images of the eye fundus, and a detecting aperture for detecting movement of laser speckles.
U.S. Pat. No. 4,854,693 discloses an ophthalmic disease detection apparatus using laser beam and slit light to illuminate the eye. Protein particles at a specific spot in the eye are detected by the light scattering they produce.
U.S. Pat. No. 4,877,322 relates to an apparatus for measuring relative oxygen saturation of the choroidal blood of the fundus. Red and infrared light beams are directed into the eye, and the reflected light beam is split into red and infrared components and their respective intensity is measured. The resulting values are compared with the intensity of the incident non-reflected red and infrared light to determine the ratio of oxyhemoglobin to reduced hemoglobin.
U.S. Pat. No. 4,485,820 discloses an oximeter for continuously monitoring hemoglobin saturation in a premature infant's eye fundus by illuminating the eye with at least two frequencies of light. The light scattered by the fundus is collected and its intensity if measured. Blood hemoglobin is calculated from the intensity of the scattered light by known methods.
U.S. Pat. No. 4,394,074 provides optical apparatus for photographing the convex surface of the iris of the eye for optimum depth of field and resolution.
U.S. Pat. No. 4,854,699 provides a noninvasive backscatter oximeter utilizing two wavelengths in the visible range and two wavelengths in the near-infrared range.
U.S. Pat. No. 4,948,248 relates to an oximeter for determining the oxygen saturation of blood.
U.S. Pat. No. 4,908,762 employs near-infrared light transmission spectrophotometry for measuring oxygenation in brain issue and organs.
U.S. Pat. No. 4,850,365 employs near infrared light for measuring body fat content.
None of the known methods for determining hemoglobin oxygenation in the blood vessels of the eye fundus can investigate the physiology of the eye while dark-adapted, a state in which the metabolic level of the retina is higher than during the light-adapted state. Light and dark induced alternations in oxygen consumption can be investigated by the technique of this invention. Such subtle alternations are a regulatory phenomenon and an important pathogenetic component of many retinal vascular diseases which comprise the leading causes of blindness. The technique of this invention can be used for clinical intervention and early diagnosis of retinal vascular diseases.